1. Field of the Invention
The present invention relates to devices capable of precisely metering a liquid. More particularly, the present invention relates to devices which deliver a precise volume of lubricant to an air tool each time the tool is cycled.
2. Description of the Prior Art
Air tool lubricators are used to deliver precise amounts of lubricant, typically oil, to air tools. They are coupled to the air line upstream of the air tool and sense airflow when the tool is cycled. Having sensed the airflow, the lubricator injects a precise volume of lubricant into the airline. For example, U.S. Pat. No. 4,450,938, issued to Davenport et al., discloses a lubricator having a single ball check design. The Davenport lubricator deposits oil directly into the air stream of the airline, and the air stream carries the lubricant to the air tool.
In other lubricators, lubricant is carried to the air tool through tubing such as 1/8" O.D. nylon. This tubing is pre-filled with lubricant and is placed within the air line supplying the air tool. Such devices are available from Master Pneumatic-Detroit, Inc., under the trade designation Servo-Meters. In these devices, air pressure on a piston pushes a metering pin into a bored hole a preset distance. This action forces lubricant through a check valve and into a lubricant line (nylon tubing). A ball check is used at the air tool so that the lubricant line remains filled with lubricant.
While the above-mentioned, prior-art devices are functional, they are not completely satisfactory. In particular, presently available devices are unsatisfactory because they still may deliver either too little or too much lubricant to an air tool. In addition, many devices of present design are undesirable because they require the use of a pre-filled lubricant line. In devices using lubricant lines, lines are pre-filled so that each metering of lubricant into the line forces an equal amount of lubricant out of the line at the other end. Lubricant lines must be carefully filled in order to avoid introducing air bubbles into them. In addition, lubricant lines may leak when not in use. For example, leaking may occur when lines are shipped from the factory to the end user. In addition, when maintenance on air tool systems is performed, the lubricant line must be disassembled and then re-filled before the device may be put back into operation.
In addition to suffering from problems associated with pre-filled lubricant lines, prior-art lubricators have at least one additional shortcoming. In general, prior-art lubricators cannot be accurately and effectively calibrated so as to adjust the metering of each lubricator in order to compensate for manufacturing variances. As is known in the art, the various components and parts of lubricators cannot be machined and assembled perfectly, but they may be constructed within certain tolerances. The variances caused by machining tolerances significantly effect lubricator operation, particularly when very precise amounts of lubricant must be metered.
Thus, it would be desirable to have an air tool lubricator that may be more effectively calibrated than prior-art devices and, therefore, deliver a more precise amount of lubricant to an air tool than prior-art devices. Further, it would also be desirable to have an air tool lubricator that does not require a pre-filled lubricant line.